A configuration has been known that performs reception processing by means of direct discrete-time sampling of a high-frequency signal with the aim of achieving a smaller receiver with lower power consumption and integrating the analog signal processer and digital signal processer (see, for example, PTL 1 and NPL 1).
FIG. 1 shows the overall configuration of a sampling circuit disclosed in PTL 1. FIG. 2 is a timing chart showing control signals inputted to the circuit shown in FIG. 1. The direct sampling circuit shown in FIG. 1 performs frequency conversion on a received analog RF (radio frequency) signal using a multi-tap direct sampling mixer to obtain a discrete-time analog signal. To be more specific, electrical charge transfer between a plurality of capacitors included in the sampling circuit in FIG. 1 realizes filter characteristics resulting in the product of an FIR (finite impulse response) filer and an IIR (infinite impulse response) filter. Characteristics around the passband are determined based on second-order IIR filter characteristics. FIG. 3A shows an example of wideband frequency characteristics and FIG. 3B shows an example of narrowband frequency characteristics around the passband.
Furthermore, a configuration based on the above-described configuration is known whose transfer function includes a complex pole (NPL 2). FIG. 4 illustrates the overall configuration of a direct sampling circuit disclosed in NPL 2. FIG. 5 is a timing chart illustrating control signals inputted to the circuit in FIG. 4. FIG. 6 is an example of frequency characteristics obtained by the circuit in FIG. 4 (local (LO) frequency fLO=2.4 GHz). The direct sampling circuit is known to obtain ripples in the passband by including a complex pole in a transfer function.